L.M. Capitán Cañadas¹, M.A. Sicilia Gutiérrez¹, S.L. Martínez Castillo², I.L. Labrot Moleón¹, D. Sánchez López², 
E. Valencia Laseca³

Recibido: 4 de julio de 2003

Aceptado: 25 de mayo de 2005

1 Médico residente.
2 Médico adjunto.
3 Jefe de Servicio.
Servicio de Cirugía Oral y Maxilofacial. Hospital Universitario Virgen de las Nieves.
Granada. España.

Luis Miguel Capitán Cañadas
Servicio de Cirugía Oral y Maxilofacial
Hospital Universitario Virgen de las Nieves. CRT.
Carretera de Jaén s/n. Granada, España
e-mail: luismxf@hotmail.com

Introduction

Tumor lesions with a parapharyngeal location are very unusual, representing between 0.5 and 0.8% of all tumors of the head and neck.^1,2 The behavior of approximately 80% is benign.^2-4 These lesions are unusual as a result of their complex anatomic position and of their appearance at the clinical onset, which is in most cases unspecific as a result nearly always of the compression effect produced by the lesion on the oro and rhinopharynx.

The anatomy of the parapharyngeal space is well known,^2,5 although we should remember the important vasculonervous network within it. The fascia that extends from the styloid process to the tensor muscle of the vellum of the palate has been the reference point traditionally for dividing the parapharyngeal space into the pre and retrostyloid areas. In the first area we find part of the deep lobe and the parotid gland and a small branch of the fifth pair of cranial nerves that crosses and provides innervation to the vellum tensor of the palate. The principal content of this space is fat and the large majority of tumors that we find here are salivary lesions, neurogenic tumors and lipomas.⁶ The retrostyloid area contains the internal carotid artery and the internal jugular vein as well as the cranial pairs of nerves IX, X, XI and XII, the sympathetic chain, lymphatic nodes and glomic tissue. In this space we may find lesions originating from any of the structures that are contained in this area.

In the classification of parapharyngeal tumors we find three groups that are arranged from larger to smaller according to the frequency with which they appear.

The most common group is made up of tumors originating in the salivary glands (40-50%), in second place are neurogenic tumors (17-25%) and the third group is made up of paragangliomas (10-15%). In the group of lesions with a neurogenic origin located in the parapharyngeal space, we find three types of lesions that are also, in decreasing order: schwannomas or neurilemomas, chemodectomas and neurofibromas.

Schwannomas are histologically benign tumors, derived from the Schwann sheath; 25-45% of schwannomas are extracranial and they appear in the head and neck, the most favored locations being laterocervial. Their clinical development is slow, which leads to a diagnosis that is tardy on most occasions. On trying to establish their diagnostic orientation it is important to rely on suitable anamnesis and imaging studies with a high resolution (Computed Axial Tomography, Nuclear Magnetic Resonance and Carotid Arteriography. The use of cytohistological diagnostic techniques continues being controversial, with biopsies being used in exceptional cases. The treatment of choice for neurilemomas is surgical excision, preceded if need be by preosurgical embolization 24-48 hours before surgery. Generally, complementary therapy is not necessary as the recurrence rate after surgery is very low. Anatomopathological study of the lesion is needed in order to confirm the diagnosis of schwannoma.

Clinical case

Female patient, 31 years old, with no medical history of interest, attended the Oral and Maxillofacial service of the University Hospital Virgen de las Nieves Granada as she had unspecific neck pain and persistent rhinolalia that had been developing for some years.

During the intraoral examination a bulging of the right lateral oropharyngeal wall was noted and the uvula was slightly displaced. There was no odynodysphagia nor was there any accompanying dyspneic sensation (fig.1) The cervical examination was not significant in any way. As a possible expansive process in the retro-pharynx was suspected, tests with Computed Axial Tomography (CT) and Nuclear Magnetic Resonance (MR) were carried out that revealed the existence of an oval mass (measuring 5 x 4 x 7 cm). It had well-defined borders and it was located in the right parapharyngeal space. The upper part had necrotic areas and it had an abundant vascular supply (figs. 2, 3a and b). The possible radiological diagnoses were compatible with a hamartomatous lesion, a lesion of a lymphoid nature, and a glomic or neurogenic lesion. With the radiological evidence of a highly vascular lesion, an arteriography of the common carotid artery was carried out together with a selective arteriography of the right external carotid artery, which showed that the mass was supplied by the right ascending pharyngeal artery (fig. 4).

With this data cyto-histological diagnostic tests were dispensed with because of a risk of bleeding, and it was decided that the lesion should be embolized as, after hormonal studies, catecholaminergic autonomous secretion was ruled out. After achieving tumoral devascularization of approximately 90%, the tumor was then removed 24 hours after embolization. Using a transcervical approach, there being no need for a mandibulotomy, the right parapharyngeal space was accessed and an encapsulated mass was observed that depended on nervous structures (low cranial nerves) that could be completely removed with total preservation of the vasculonervous network (fig. 5).

Macroscopically it was a solid mass with a brownish color. It had an elastic consistency and measured 7.8 x 5.5 x 5 cm. On cutting into it, cystic necrotic areas appeared. The diagnosis of the lesion by histological study of the surgical sample was of a mixed schwannoma (Antoni A and B) (fig. 6).

After a follow-up of the patient of eleven months there appeared to be a clinical and radiological remission of the process (figs. 7 and 8).

Discussion

All the articles revised^1,2,4,7 are in agreement as to the classification of the tumor masses of the pharyngeal space into three groups: salivary gland tumors: originating principally in the deep parotid lobe, neurogenic tumors: mostly schwannomas or neurilemomas and paragangliomas. To a lesser extent are described,^2,4 a fourth miscellaneous group that includes different types of lesions: hemangiomas, branchial cysts, lymphatic nodes, tumor metastases, aneurisms, chordomas, meningiomas and sarcomas. Within regard to neurogenic tumors, the most common group consists in schwannomas or neurilemomas, followed in order of frequency by chemodectomas and neurofibromas. ² First described in 1910 by Verocay (in Ortiz- Hidalgo, 2004)⁸ and histologically typified by Antoni⁹ in 1920, schwannomas or neurilemomas are tumors that originate in the nervous sheath that covers the axons of the peripheral nervous system or Schwann sheath. According to the histological characteristics, we find two groups: Antoni A, which is characterized a dense groups of Schwann cells with nuclear palisading leading to formations that are typically called Verocay bodies, and Antoni B. These tend to be hypocellular and their arrangement is clearly irregular. In 47% of cases, the schwannomas found are mixed in shape,¹⁰ (Antoni A and B). Other histological varieties have been described much less frequently, ¹¹ (melanotic or angiomatous schwannomas). Of the schwannomas, 10% are extracranial and of these 25-45% appear in the head and neck,^2,12 principally in the laterocervical area. Of the parapharyngeal neurilemomas, 50% originate in the vagus nerve,^2,13 with the cervical sympathetic chain being the second most common location for schwannomas.¹⁴ There is no predominant age range associated with the appearance of this type of lesion. In the distribution according to sex neither of the two types appears to predominate. Authors such as Torossian and Gilmer-Hill,^10,15 report a predominance in females; Hood,¹⁶ documented a greater frequency in males and, in Peter Pang and Maran’s series^1,5 they appeared equally in the male and female population with male-female ratios of 15:16 and 14:15 respectively. Predisposition and risk factors do not appear to have been found.¹⁰ In young patients with schwannomas the existence of type II nerofibromatosis,¹⁰ should be ruled out.

These tumors are generally benign,^2,3 although the presence of pain or nerve damage should alert us to a possible malignant transformation.^2,7 Their clinical behavior is silent, there tending to be an association with a phenomena of secondary compression as a result of the progressive and slow growth of the tumor. The most common symptom,^2,7,10 is the presence of a slow growing, painless mass, although on certain occasions the clinical behavior of other pathologies such as tumor metastases or infectious processes can be copied.7 The nerve of origin is not normally affected, and symptoms as a result of nerve damage are not very common. In patients with schwannomas that have been evolving for a long time, slight reversible neurological deficiencies have been described.¹⁷

Although the diagnostic protocol and therapeutic management of neurilemomas coincides generally with the rest of the parapharyngeal tumors,^2,18 it should be checked individually together with all the details linked to this type of lesion.

With regard to the diagnosis of parapharyngeal neurogenic tumors, most authors consider the use of imaging techniques, principally Nuclear Magnetic Resonance, ¹⁹ and Computed Axial Tomography,^1,20,21 as being of fundamental importance. NMR with gadolinium is possibly the radiological technique of choice,^19,20,22 as it allows locating the tumor in the pre or retrostyloid compartment, studying the relationship with vasculonervous structures beside it, and identifying more precisely the particular characteristics of the lesion (degree of vascularization, consistency, size). The images obtained with the CT scan allow studying the relationship with the skull base.^2,21 The use of arteriographies for diagnostic purposes is advised when there is a radiological suspicion of highly vascularized lesions.²³ Cytohistological study by means of fine needle aspiration (FNA) can provide significant data,^2,24 and it is used only for tumors when we are sure of the mass being solid, once the imaging techniques previously mentioned have been used. The transoral approach,^24,25 is suggested as the most appropriate. In a recent series of 24 cases published by Oliai et al,²⁴ no complications were described following FNA diagnosis of a parapharyngeal mass that was non-vascular (the cytological diagnosis was of schwannoma). The use of a presurgical biopsy is contraindicated in most instances,² due to the anatomical complexity of the approach, the risk of rupture and intratumor hemorrhage, and of the possibility of creating a fibrous adherence between the capsule of the tumor and the mucosa of the pharyngeal wall leading to difficulties with the later removal of the tumor.

With regard to neurilemomas with abundant vascularization, it may be necessary to use a presurgical embolization technique, ^20,23 due to the risk of intraoperative hemorrhaging as well as damage to vasculonervous structures adjacent to the tumor, so that surgical morbidity is, as a result, considerably reduced. In those cases where we are not completely sure of the lesion being a schwannoma, and in order to prepare for a possible diagnosis of paranganglioma, it may be convenient to rule out the autonomous catecholaminergic secretion of the tumor,²⁶ (more specifically, with a urine test for vanillymandelic acid, metanephrines, dopamine, epinephrine and norepinephrine and determining the plasma level of the catecholamines,^27,28 before carrying out embolization, so that the appearance of possible symptoms of hypertension and arrhythmias during the surgical procedure, which are difficult to control,²⁰ are avoided.

The treatment of choice is the surgical removal of the tumor,^{1,2,4,7,10,16,20} and although various methods of approach are proposed (transoral,^2,29 transcervical with or without a mandibulectomy,^2,30 cervicoparotid,¹⁸ transparotid,31 or cervico- transpharyngeal),18 most authors coincide as to the transcervical approach being the most appropriate,^2,10,20,32 and the one with better surgical results.¹ In certain cases such as with elderly patients or those with a systemic pathology where the use of anesthesia is contraindicated, in cases of tumors that cannot be resectioned or in cases of patients that will not accept the intraoperative morbidity that the surgery involves, treatment with radiotherapy can be opted for.^2,20

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